1. Field of the Invention
Present invention relates to an end face polished ferrule and its method of manufacture. It also relates particularly to a end face polished ferrule and its method of manufacture for improving the connection characteristics of optical fibers in assemblies of the sort used in analog image communications like CATV(CAble TeleVision), very high speed communications and optical amplifiers, or optical fiber assemblies having isolator functions.
2. Description of the Prior Art
The prior art for connecting two optical fibers assemblies, comprising of an optical fiber and a ferrule, with a small connection loss and little light reflected back to the source has been proposed in publications of Laid-open Japanese Patent Application Nos. 87111/1986 and 121805/1989. The objective is achieved by polishing the end faces of both of said optical fiber assemblies to an oblique convex spherical surface and then connecting said optical assemblies by bringing the oblique convex spherical surfaces in contact with each other.
For example, as shown in FIG. 17, to connect the optical fiber assemblies (formed by an optical fiber s and a ferrule 150 and an optical fiber s' and a ferrule 150'), the end faces of said optical fiber assemblies are polished to form oblique spherical surfaces q and q' in such a way that, the line joining the centers of curvature C and C' of said oblique spherical surfaces q and q' makes an angle of 8.degree. with respect to the optical axes L3 and L3' of said optical fibers s and s'.
The foregoing method improves the coincidence of the optical axes of the fibers s and s' and enables light reflected back to the source to be minimized.
In conventional optical connector end-face polishing methods, the convex spherical surface q is formed according to the procedure mentioned below.
In the beginning, as shown in FIG. 18(a), an optical assembly is formed by bonding a fiber s and a conically tapered ferrule 150 with a reinforced adhesive.
Next, as shown in FIG. 18(b), said optical fiber assembly is rotated around a vertical axis of rotation after inclining it by an angle of 8.degree. on a polishing disc (not shown in the figure), thereby forming an oblique horizontal surface 151 at the tip of the optical fiber assembly. Because the tip of the ferrule 150 is cut into a conical shape, 151t, the center of the oblique horizontal surface 151 is offset from the point P where the optical axis of the optical fiber s intersects with the surface 151.
Hereafter, as shown in FIG. 18(c), said optical fiber assembly in its inclined position is rotated around a vertical axis of rotation on a polishing disc with an elastic abrasive disc mounted (not shown in the figure) on it, thereby forming a oblique convex spherical surface q at the tip of it.
In the aforementioned conventional end face polished optical fiber assembly, qt, the center of the oblique convex spherical surface q is offset from the point P as shown in FIG. 19, because the position of qt, the center of said surface affects 151t, the center of the horizontal surface 151, and because the contact with the polishing disc mounted with an elastic abrasive disc creates an unbalance due to the inclination of the ferrule f (for instance, when the angles at the corners 150a and 150b are different). Due to this, stabilization and minimization of insertion loss and light reflected back to the source becomes difficult.